The present invention relates to a new and improved apparatus for monitoring lap or coil formation or the like on a roll of a pair of rolls guiding a slubbing or sliver in a textile machine, especially a spinning machine, comprising pressing means for pressing one or a first roll against a second roll or a sliver-guiding element moved in analogous manner.
In an apparatus as know to the art, for example, from European Patent No. 0,062,185, published Feb. 26, 1986, and its cognate U.S. Pat. No. 4,413,378, granted Nov. 8, 1983, pressure rolls are pressed at both ends thereof by means of pneumatic cylinders against the drive rolls in order to produce the required clamping force between the pressure rolls and the drive rolls.
In the event of lap formation or coiling occurring either on the pressure roll or on the drive roll, the pressure cylinder moves back in a direction opposite to the direction of pressing.
In combination with drafting arrangements or systems of this kind, it is known to detect any receding or reverse movement of the pressure roll by means of suitable and appropriately arranged limit switches and to thus stop the drafting arrangement or system.
It is also known that pressure rolls of this kind have to be ground from time to time at their cylindrical surface guiding the slubbing or sliver in order to remove grooves forming therein as a result of the drafting operation. This grinding operation reduces the diameter of the pressure rolls, so that the contact travel to the aforementioned limit switch increases such that the lap or coil forming on the pressure roll or on the drive roll has to be of a larger diameter if it is to stop the drafting arrangement.
It is further known that limit switches of this type can be manually moved in order to maintain the aforementioned switching travel within the required limits to some extent.
However, shifting the limit switches in this way depends, on the one hand, on the operator's reliability and dexterity and requires, on the other hand, reliable determination of the new diameter of the roll.